1. Field of the Invention
The present invention relates to a wafer cassette conveying system in a semiconductor producing apparatus.
2. Description of the Relevant Art
Conventionally, there is disclosed in the official gazette of Japanese Patent Application Laid Open (Kokai) 2-39450, a wafer cassette conveying system comprising trays on which are temporarily placed wafers, disposed respectively on a carrying-in port and a carrying-out port of a treating room disposed in a sheet treating device, thereby improving an efficiency of conveying the wafer cassette to the sheet treating device. FIG. 4 is a schematic configuration view of the wafer cassette conveying system in the sheet treating device which is provided with one treating room. In FIG. 4, reference numeral 1 designates the sheet treating device which is provided with a first wafer cassette space 2a, a first tray 3a, a treating room 4, a second tray 3b, and a second wafer cassette space 2b in the order named. Untreated wafers and treated wafers are placed temporarily on the first tray 3a and the second tray 3b mentioned above. Hereinafter, the wafer cassette which stores the wafers and the wafer cassette which does not store the wafers are referred to as "the actual cassette" and "the empty cassette", respectively.
In the above-described construction, the actual cassettes (two actual cassettes in FIG. 4), which store untreated wafers, are carried therein, then conveyed to the first cassette space 2a. The untreated wafers stored in one of the actual cassettes are transferred to the treating room 4 to be treated thereat, and then transferred to the second tray 3b in order. During this treatment, the other untreated wafers are transferred to the first tray 3a from the other of the actual cassettes placed on the first cassette space 2a. The above-mentioned two of the actual cassettes, from which the untreated wafers stored therein are taken out, become the empty cassettes. These two of the empty cassettes are transferred to the second wafer cassette space 2b. The treated wafers placed on the second tray 3b are stored in one of the empty cassettes. The untreated wafers placed on the first tray 3a are loaded into the treating room 4 to be treated thereat, then stored in the other of the empty cassettes through the second tray 3b.
As mentioned above, the description is made to a wafer cassette conveying system comprising trays on which are temporarily placed wafers, disposed respectively on a carrying-in port and a carrying-out port of a treating room disposed in a sheet treating device, thereby improving an efficiency of conveying the wafer cassette to the sheet treating device. There will be described hereinbelow a wafer cassette conveying system having a plurality of treating rooms. FIG. 5 is a configuration view of a conventional wafer cassette conveying system having a plurality of treating rooms. In FIG. 5, reference numerals 11, 12 and 13 designate a first treating device, a second treating device and a third treating device, respectively.
The first treating device 11 has a carrying-in cassette space 11a on which are temporarily placed a wafer cassette to be carried therein and a carrying-out cassette space 11b on which are temporarily placed an actual cassette storing the treated wafers therein. The first treating device 11 is comprised of, for example, a stocker, an inspection receiving stand, a cleaning device and an etching device and so on. Also, the first treating device 11 outputs a lot carrying-out request signal, indicative of carrying the wafer cassette into the second treating device 12 when the actual cassette storing the treated wafers is placed on the carrying-out cassette space 11b.
The second treating device 12 is provided with a plurality of treating portions 12-1 to 12-3. There are carried out at these treating portions 12-1 to 12-3, for example, a first cleaning treatment, a drying treatment, a second cleaning treatment and the like. Also, there are arranged at the second treating device 12 a carrying-in cassette space 12a on which are temporarily placed the carried-in wafer cassette and a carrying-out cassette space 12b temporarily placed the empty cassette which has stored the wafers having completed the respective treatments at the treating portions 12-1 to 12-3. At the second treating device 12, the wafers are transferred from the actual cassette placed on the carrying-in cassette space 12a to the respective treating portions 12-1 to 12-3 to thereby be treated thereat. Therefore, after all the wafers has been transferred, the above-mentioned actual cassette becomes empty. Also, when the treatment of the treating portion 12-3 is being carried out, the empty cassette must be placed on the carrying-out cassette space 12b previously, in order to store therein the wafers having completed the treatment at the treating portion 12-3.
Further, the second treating device 12 outputs an empty cassette carrying-out request signal indicative of carrying-out the empty cassette, when the actual cassette placed on the carrying-in cassette space 12a from which all the wafers have been transferred becomes the empty cassette, and also outputs a cassette carrying-in request signal indicative of carrying the empty cassette into the carrying-out cassette space 12b, when the actual cassette on the carrying-out cassette space 12b are carried out. Besides, the second treating device 12 outputs a lot carrying-out request signal, when the empty cassette placed on the carrying-out cassette space 12b becomes the actual cassette to which have been stored the wafers having completed the treatment at the treating portion 12-3.
Reference numeral 14 designates a cassette space arranged in the vicinity of the second treating device 12, on which the empty cassette is temporarily placed, when the actual cassette placed on the carrying-in cassette space 12a in the second treating device 12, from which all the wafers have been loaded to the treating portion 12-1, becomes the empty cassette. The empty cassette space 14 is provided with an empty cassette stand 14a on which can be placed several units of one or two cassettes, and on which can be delivered an empty cassette between operations by a conveying device 16 which will be described later.
Reference numeral 13 designates the third treating device such as, for example, a stocker, an inspection stand, a cleaning device, an etching device and the like. The third treating device 13 is provided with a carrying-in cassette space 13a on which the carried-in cassette is temporarily placed and a carrying-out cassette space 13b on which the cassette having completed treatment is temporarily placed. Further, the respective time periods required for the treatment in the first treating device 11, the second treating device 12, and the third treating device 13 are different from one another.
Reference numeral 15 designates a control device 15, being comprised of a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory) and the like, which controls the conveying device 16 based on a program stored in the ROM, the lot carrying-out request signal outputted from the first treating device 11, and the empty cassette carrying-out request signal, the lot carrying-in request signal, the empty cassette carrying-in request signal and the lot carrying-out request signal outputted from the second treating device 12. The conveying device 16 is provided with an arm for seizing the wafer cassette, and moves along a rail 17 to convey the wafer cassette. It takes a moving time period t1 for the conveying device 16 to move between the carrying-out cassette space 11b in the first treating device 11 and the empty cassette stand 14a on the cassette space 14, a moving time period t.sub.2 between the empty cassette stand 14a on the cassette space 14 and the carrying-in cassette space 12a in the second treating device 12, a moving time period t.sub.3 between the carrying-in cassette space 12a in the second treating device 12 and the carrying-out cassette space 12b in the second treating device 12, and a moving time period t.sub.4 between the carrying-out cassette space 12b in the second treating device 12 and the carrying-in cassette space 13a in the third treating device 13.
An operation of the wafer cassette conveying system having the above-described construction will now be described with reference to FIG. 6 and FIG. 7. FIG. 6 is an explanatory view for an operation of the conveying device 16 according to the conventional wafer cassette conveying system, FIG. 7 is a flowchart showing a communicating condition between the control device 15 and the conveying device 16. Firstly, in an initial state, it is assumed that all of the first treating device 11, the second treating device 12, and the third treating device 13 perform treatments of the wafer, respectively, the actual cassettes are placed on the carrying-in cassette space 11a, 12a and 13a in the respective treating devices, and that the empty cassettes are placed on the carrying-out cassette space 11b, 12b and 13b in the same. Further, it is also assumed that the conveying device 16 is on standby at a location of the carrying-in cassette space 12a in the second treating device 12.
In the second treating device 12, when all the wafers are loaded to the treating portion 12-1 from the actual cassette placed on the carrying-in cassette space 12a, the second treating device 12 outputs the empty cassette carrying-out request signal to the control device 15 (step SA1). The control device 15, when receiving this empty cassette carrying-out request signal, outputs an empty cassette conveying command signal to the conveying device 16 (step SA2). The conveying device 16, when receiving this empty cassette conveying command signal, moves at a location of the empty cassette stand 14a while seizing the empty cassette placed on the carrying-in cassette space 12a and then places the empty cassette seized by itself on the empty cassette stand 14a, during which movement is required a time period t.sub.2. The conveying device 16, when having completed this treatment, outputs a treatment completion signal to the control device 15 (step SA3). After this process, the conveying device 16 is on standby until the next command signal is outputted from the control device 15. The second treating device 12 outputs the lot carrying-in request signal to the control device 15, when the empty cassette is carried-out from the carrying-in cassette space 12a (step SA4).
Next, when the first treating device 11 has completed the treatment, then the empty cassette placed on the carrying-out cassette space 11b becomes the actual cassette to which have been stored the treated wafers, the first treating device 11 outputs the lot carrying-out request signal. The control device 15, when receiving this lot carrying-out request signal, outputs a lot carrying-in command signal to the conveying device 16 (step SA5). The conveying device 16, when receiving the lot carrying-in command signal, moves from a location of the empty cassette stand 14a to a location of the carrying-out cassette space 11b in the first treating device 11, during which movement is required a time period t.sub.1. The conveying device 16, while seizing the actual cassette placed on the carrying-out cassette space 11b, moves to the carrying-in cassette space 12a in the second treating device 12, during which movement is required a time period t.sub.1 +t.sub.2. The conveying device 16 places the actual cassette seized by itself on the carrying-in cassette space 12a in the second treating device 12. The conveying device 16, after having completed this treatment, is on standby at space 12b until the next command signal is outputted from the control device 15. The movement from space 12a to space 12b is time period t.sub.3.
In the second treating device 12, the wafers stored in the actual cassette placed on the carrying-in cassette space 12a are loaded to the treating portion 12-1, and the last wafers, which have been loaded from the actual cassette placed on the carrying-in cassette space 12a to the treating portion 12-1 and treated in the treating portions 12-2 and 12-3, are stored in the empty cassette placed on the carrying-out cassette space 12b. The second treating device 12 outputs a lot carrying-out request signal, when all these wafers are stored in the empty cassette (step SA6). The control device 15, when receiving the lot carrying-out request signal, outputs the lot carrying-out command signal to the conveying device 16 (step SA7), then the conveying device 16, while seizing the actual cassette placed on the carrying-out cassette space 12b, moves to a location of the carrying-in cassette space 13a in the third treating device 13, during which movement is required a time period t.sub.4. The conveying device 16, when having completed the movement, places the actual cassette seized by itself on the carrying-in cassette space 13a. The second treating device 12, after having completed the treatment, outputs the empty cassette carrying-in request signal (step SA8).
The control device 15, when receiving the above empty cassette carrying-in request signal, outputs an empty cassette carrying-in command signal to the conveying device 16 (step SA9). The conveying device 16, when receiving this empty cassette carrying-in command signal, moves to a location of the empty cassette stand 14a, during which movement is required a time period t.sub.2 +t.sub.3 +t.sub.4. The conveying device 16, while seizing the empty cassette placed on the empty cassette stand 14a, moves to a location of the carrying-out cassette space 12b in the second treating device 12 and places the empty cassette seized by itself thereon. The conveying device 16, after having completed this treatment, moves to a location of the carrying-in cassette space 12a in the second treating device 12, whereby the operation of the one cycle has been completed.
In the operation of the one cycle mentioned above, the control device 15 outputs four time-commands to the conveying device 16, so that the time period required for the movement of the conveying device 16 is calculated by the use of the following equation: EQU t.sub.2 +t.sub.1 +(t.sub.1 +t.sub.2)+t.sub.3 +t.sub.4 +(t.sub.2 +t.sub.3 +t.sub.4)+t.sub.2 +t.sub.3 =2t.sub.1 +4t.sub.2 +3t.sub.3 +2t.sub.4.
As described above, according to the conventional wafer cassette conveying system, the conveying device 16 conveys the empty cassette or the actual cassette while seizing the same. When the conveying device 16 carries in and carries out the empty cassette to the second treating device 12, the second treating device 12 outputs the empty cassette carrying-in request signal and the empty cassette carrying-out request signal, respectively, and then the control device 15 outputs the empty cassette carrying-in command signal and the empty cassette carrying-out command signal to the conveying device 16. After receiving these signals, the conveying device 16, when conveying the empty cassette to the second treating device 12, has to move to a location of the empty cassette stand 14a, seize the empty cassette and carry-in the same into the second treating device 12, also, when carrying-out the empty cassette from the second treating device 12, has to convey the empty cassette in the second treating device 12 to a location of the empty cassette stand 14a. Therefore, there are problems that the communications between the control device 15 and the conveying device 16 are generated too frequently, and that the time period required for the movement of the conveying device 16 is made long.
Also, there is disclosed in the official gazette of Japanese Patent Application Laid Open (Kokai) No. 7-283093 a technique which improves the conveying efficiency. In the technique described in the above gazette, there is no empty cassette between respective treating devices, a plurality of treating devices are concentrated and conveying passages for exclusive use of carrying vehicles are disposed between the respective treating devices. In this technique, the wafer cassette travels depending on the condition of the treatments in the respective treating devices. Also, there are problems in this technique that the conveying passages for exclusive use, a conveying/moving mechanism and a conveying passage controlling mechanism are required, so the system is increased in cost and the respective treating devices cannot be used unless they are not suitable for the above conveying passage controlling mechanism, compared with the above-mentioned case where the empty cassette space is provided.